1) Field of the Invention
This invention relates to an emulsion fuel engine which uses an emulsion fuel as a fuel, and more specifically to an emulsion fuel engine with reduced combustion noise and extended service life for the injection system components.
2) Description of the Related Art
To produce less exhaust gas and reduce the specific fuel consumption, diesel engines using an emulsion fuel are known. The term "emulsion fuel" as used herein mean a fuel formed by emulsifying mutually-insoluble fuels, for example, water and diesel fuel, water and heavy oil, or methanol and diesel fuel.
Referring to FIG. 10, the construction of a conventional emulsion fuel engine will be described. In FIG. 10, numeral 1 indicates a fuel tank in which an emulsion fuel (for example, water and diesel fuel) is stored. Arranged between the fuel tank 1 and an injection pump 2 is a fuel pipe FP which is provided with a fuel pump 3 for delivering the emulsion fuel and also with a fuel filter 4.
The injection pump 2 is provided with a reciprocating plunger 7 which moves up and down as a camshaft 5 rotates together with a cam 6. The injection pump 2 begins to draw the fuel after an upper end face of the plunger 7 has come to a position lower than a fuel draw/spill port 9. After the upper end face of the plunger 7 has moved to a position above the fuel draw/spill port 9, the injection pump 2 begins to deliver the fuel under pressure. When a lead 10 formed in a peripheral wall of the plunger 7 has overlapped the fuel draw/spill port 9, the injection pump 2 terminates the delivery of the fuel under pressure. Designated at numeral 11 is a delivery valve for the prevention of a reverse flow.
An injection pipe IP is arranged between a top portion of the injection pump 2 and an injection nozzle 12. A fuel feed channel 13 is formed inside the injection nozzle 12. Through the fuel feed channel 13, the fuel which has been delivered under pressure from the injection pipe IP is guided to a lower part of the nozzle 12. A needle valve 14 is lifted by the pressure of the fuel, whereby the fuel is injected into the combustion chamber through injector holes 15.
The fuel discharged from the injection pump 2 and the injection nozzle 12 is returned to the fuel tank 1 via a fuel return pipe 16.
An emulsion fuel has poor ignitability in a cylinder so that ignition delay is prolonged. The fuel is therefore injected in quantity until it is ignited. Since this fuel then burns at once at the time of ignition, the pressure inside the cylinder increases at a high rate and, accordingly, combustion noise tends to occur.
In conventional emulsion fuel engines, an emulsion fuel prepared in advance is merely stored in the fuel tank 1 instead of diesel fuel.
A diesel engine injection system includes many parts operating in the fuel with micron-level clearances. An emulsion fuel with enclosed water droplet induces excess wear due to insufficient lubrication and rusting at the injection pump 2, resulting in the problem that the durability of the injection pump 2 is reduced.
At the injection nozzle 12, the injector holes 15 may be clogged by abraded particles formed by the excessive wear, leading to the problem that the durability of the injection nozzle 12 is reduced.